MicroRNA-183-5p Increases with Age in Bone-Derived Extracellular Vesicles, Suppresses Bone Marrow Stromal (Stem) Cell Proliferation, and Induces Stem Cell Senescence

Multifaceted Mechanisms of Vascular Calcification in Aging

Approximately 20% of the world’s population will be around or above 65 years of age by the next decade. Out of these, 40% are suspected to have cardiovascular diseases as a cause of mortality. Arteriosclerosis, characterized by increased vascular calcification, impairing Windkessel effect and tissue perfusion, and determining end-organ damage, is a hallmark of vascular pathology in the elderly population. Risk factors accumulated during aging affect the normal physiological and vascular aging process, which contributes to the progression of arteriosclerosis. Traditional risk factors, age-associated diseases, and respective regulating mechanisms influencing vascular calcification and vascular stiffness have been extensively studied for many years. Despite the well-known fact that aging alone can induce vascular damage, specific mechanisms that implicate physiological aging in vascular calcification, contributing to vascular stiffness, are poorly understood. This review focuses on mechanisms activated during normal aging, for example, cellular senescence, autophagy, extracellular vesicles secretion, and oxidative stress, along with the convergence of premature aging models’ pathophysiology, such as Hutchinson-Gilford Progeria (prelamin accumulation) and Klotho deficiency, to understand vascular calcification in aging. Understanding the mechanisms of vascular damage in aging that intersect with age-associated diseases and risk factors is crucial to foster innovative therapeutic targets to mitigate cardiovascular disease.

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Roles for miRNAs in osteogenic differentiation of bone marrow mesenchymal stem cells

Bone marrow mesenchymal stem cells (BMSCs), which were first discovered in bone marrow, are capable of differentiating into osteoblasts, chondrocytes, fat cells, and even myoblasts, and are considered multipotent cells. As a result of their potential for multipotential differentiation, self-renewal, immune regulation, and other effects, BMSCs have become an important source of seed cells for gene therapy, tissue engineering, cell replacement therapy, and regenerative medicine. MicroRNA (miRNA) is a highly conserved type of endogenous non-protein-encoding RNA of about 19-25 nucleotides in length, whose transcription process is independent of other genes. Generally, miRNA plays roles in regulating cell proliferation, differentiation, apoptosis, and development by binding to the 3' untranslated region of target mRNAs, whereby they can degrade or induce translational silencing. Although miRNAs play a regulatory role in various metabolic processes, they are not translated into proteins. Several studies have shown that miRNAs play an important role in the osteogenic differentiation of BMSCs. Herein, we describe in-depth studies of roles for miRNAs during the osteogenic differentiation of BMSCs, as they provide new theoretical and experimental rationales for bone tissue engineering and clinical treatment.

Radiation-Induced Bystander Effect is Mediated by Mitochondrial DNA in Exosome-Like Vesicles

Exosome-like vesicles (ELV) are involved in mediating radiation-induced bystander effect (RIBE). Here, we used ELV from control cell conditioned medium (CCCM) and from 4 Gy of X-ray irradiated cell conditioned medium (ICCM), which has been used to culture normal human fibroblast cells to examine the possibility of ELV mediating RIBE signals. We investigated whether ELV from 4 Gy irradiated mouse serum mediate RIBE signals. Induction of DNA damage was observed in cells that were treated with ICCM ELV and ELV from 4 Gy irradiated mouse serum. In addition, we treated CCCM ELV and ICCM ELV with RNases, DNases, and proteinases to determine which component of ELV is responsible for RIBE. Induction of DNA damage by ICCM ELV was not observed after treatment with DNases. After treatment, DNA damages were not induced in CCCM ELV or ICCM ELV from mitochondria depleted (ρ0) normal human fibroblast cells. Further, we found significant increase in mitochondrial DNA (mtDNA) in ICCM ELV and ELV from 4 Gy irradiated mouse serum. ELV carrying amplified mtDNA (ND1, ND5) induced DNA damage in treated cells. These data suggest that the secretion of mtDNA through exosomes is involved in mediating RIBE signals.

Multifaceted Mechanisms of Vascular Calcification in Aging

Approximately 20% of the world's population will be around or above 65 years of age by the next decade. Out of these, 40% are suspected to have cardiovascular diseases as a cause of mortality. Arteriosclerosis, characterized by increased vascular calcification, impairing Windkessel effect and tissue perfusion, and determining end-organ damage, is a hallmark of vascular pathology in the elderly population. Risk factors accumulated during aging affect the normal physiological and vascular aging process, which contributes to the progression of arteriosclerosis. Traditional risk factors, age-associated diseases, and respective regulating mechanisms influencing vascular calcification and vascular stiffness have been extensively studied for many years. Despite the well-known fact that aging alone can induce vascular damage, specific mechanisms that implicate physiological aging in vascular calcification, contributing to vascular stiffness, are poorly understood. This review focuses on mechanisms activated during normal aging, for example, cellular senescence, autophagy, extracellular vesicles secretion, and oxidative stress, along with the convergence of premature aging models' pathophysiology, such as Hutchinson-Gilford Progeria (prelamin accumulation) and Klotho deficiency, to understand vascular calcification in aging. Understanding the mechanisms of vascular damage in aging that intersect with age-associated diseases and risk factors is crucial to foster innovative therapeutic targets to mitigate cardiovascular disease. Visual Overview- An online visual overview is available for this article.

miR-384-5p Targets Gli2 and Negatively Regulates Age-Related Osteogenic Differentiation of Rat Bone Marrow Mesenchymal Stem Cells

Aberrant microRNA expression correlates with age-related osteoporosis, which impairs bone formation by regulating osteoblastic activity, thus leading to age-related bone loss. In this study, we observed that miR-384-5p was significantly upregulated in bone marrow mesenchymal stem cells (BMSCs) from aged rats compared with BMSCs from young rats. In vitro functional assays revealed that overexpression of miR-384-5p in young BMSCs inhibited osteogenic differentiation and accelerated senescence, whereas knockdown of miR-384-5p in aged BMSCs had the opposite effects. Furthermore, we demonstrated that miR-384-5p inhibited the expression of Gli2 at both the mRNA and protein levels by directly binding to the 3' untranslated region of Gli2 mRNA. The osteogenic capacity of Gli2-knockdown BMSCs was rejuvenated by miR-384-5p inhibition. Finally, in vivo assays showed that the inhibition of miR-384-5p prevented bone loss and increased the osteogenic capacity in aged rats. Overall, our study suggests that miR-384-5p functions as a negative regulator of osteogenesis, indicating that the inhibition of miR-384-5p may be a therapeutic strategy against age-related bone loss.

Muscle-derived miR-34a increases with age in circulating extracellular vesicles and induces senescence of bone marrow stem cells

Extracellular vesicles (EVs) are known to play important roles in cell-cell communication. Here we investigated the role of muscle-derived EVs and their microRNAs in the loss of bone stem cell populations with age. Aging in male and female C57BL6 mice was associated with a significant increase in expression of the senescence-associated microRNA miR-34a-5p (miR-34a) in skeletal muscle and in serum -derived EVs. Muscle-derived, alpha-sarcoglycan positive, EVs isolated from serum samples also showed a significant increase in miR-34a with age. EVs were isolated from conditioned medium of C2C12 mouse myoblasts and primary human myotubes after cells were treated with hydrogen peroxide to simulate oxidative stress. These EVs were shown to have elevated levels of miR-34a, and these EVs decreased viability of bone marrow mesenchymal (stromal) cells (BMSCs) and increased BMSC senescence. A lentiviral vector system was used to overexpress miR-34a in C2C12 cells, and EVs isolated from these transfected cells were observed to home to bone in vivo and to induce senescence and decrease Sirt1 expression of primary bone marrow cells ex vivo. These findings suggest that aged skeletal muscle is a potential source of circulating, senescence-associated EVs that may directly impact stem cell populations in tissues such as bone via their microRNA cargo.

Inhibition of Osteocyte Membrane Repair Activity via Dietary Vitamin E Deprivation Impairs Osteocyte Survival

Osteocytes experience plasma membrane disruptions (PMD) that initiate mechanotransduction both in vitro and in vivo in response to mechanical loading, suggesting that osteocytes use PMD to sense and adapt to mechanical stimuli. PMD repair is crucial for cell survival; antioxidants (e.g., alpha-tocopherol, also known as Vitamin E) promote repair while reactive oxygen species (ROS), which can accumulate during exercise, inhibit repair. The goal of this study was to determine whether depleting Vitamin E in the diet would impact osteocyte survival and bone adaptation with loading. Male CD-1 mice (3 weeks old) were fed either a regular diet (RD) or Vitamin E-deficient diet (VEDD) for up to 11 weeks. Mice from each dietary group either served as sedentary controls with normal cage activity, or were subjected to treadmill exercise (one bout of exercise or daily exercise for 5 weeks). VEDD-fed mice showed more PMD-affected osteocytes (+ 50%) after a single exercise bout suggesting impaired PMD repair following Vitamin E deprivation. After 5 weeks of daily exercise, VEDD mice failed to show an exercise-induced increase in osteocyte PMD formation, and showed signs of increased osteocytic oxidative stress and impaired osteocyte survival. Surprisingly, exercise-induced increases in cortical bone formation rate were only significant for VEDD-fed mice. This result may be consistent with previous studies in skeletal muscle, where myocyte PMD repair failure (e.g., with muscular dystrophy) initially triggers hypertrophy but later leads to widespread degeneration. In vitro, mechanically wounded MLO-Y4 cells displayed increased post-wounding necrosis (+ 40-fold) in the presence of H2O2, which could be prevented by Vitamin E pre-treatment. Taken together, our data support the idea that antioxidant-influenced osteocyte membrane repair is a vital aspect of bone mechanosensation in the osteocytic control of PMD-driven bone adaptation.

Extracellular vesicles in bone: "dogrobbers" in the "eternal battle field"

Throughout human life, bone is constantly in a delicate dynamic equilibrium of synthesis and resorption, hosting finely-tuned bone mineral metabolic processes for bone homeostasis by collaboration or symphony among several cell types including osteoclasts (OCs), osteoblasts (OBs), osteocytes (OYs), vascular endothelial cells (ECs) and their precursors. Beyond these connections, a substantial level of communication seems to occur between bone and other tissues, and together, they form an organic unit linked to human health and disease. However, the current hypothesis, which includes growth factors, hormones and specific protein secretion, incompletely explains the close connections among bone cells or between bone and other tissues. Extracellular vesicles (EVs) are widely-distributed membrane structures consisting of lipid bilayers, membrane proteins and intravesicular cargo (including proteins and nucleic acids), ranging from 30 nm to 1000 nm in diameter, and their characters have been highly conserved throughout evolution. EVs have targeting abilities and the potential to transmit multidimensional, abundant and complicated information, as powerful and substantial "dogrobbers" mediating intercellular communications. As research has progressed, EVs have gradually become thought of as "dogrobbers" in bone tissue-the "eternal battle field" -in a delicate dynamic balance of destruction and reconstruction. In the current review, we give a brief description of the major constituent cells in bone tissues and explore the progress of current research on bone-derived EVs. In addition, this review also discusses in depth not only potential directions for future research to breakthrough in this area but also problems existing in current research that need to be solved for a better understanding of bone tissues.

Bone Marrow Derived Extracellular Vesicles Activate Osteoclast Differentiation in Traumatic Brain Injury Induced Bone Loss

Traumatic brain injury (TBI) is a major source of worldwide morbidity and mortality. Patients suffering from TBI exhibit a higher susceptibility to bone loss and an increased rate of bone fractures; however, the underlying mechanisms remain poorly defined. Herein, we observed significantly lower bone quality and elevated levels of inflammation in bone and bone marrow niche after controlled cortical impact-induced TBI in in vivo CD-1 mice. Further, we identified dysregulated NF-κB signaling, an established mediator of osteoclast differentiation and bone loss, within the bone marrow niche of TBI mice. Ex vivo studies revealed increased osteoclast differentiation in bone marrow-derived cells from TBI mice, as compared to sham injured mice. We also found bone marrow derived extracellular vesicles (EVs) from TBI mice enhanced the colony forming ability and osteoclast differentiation efficacy and activated NF-κB signaling genes in bone marrow-derived cells. Additionally, we showed that miRNA-1224 up-regulated in bone marrow-derived EVs cargo of TBI. Taken together, we provide evidence that TBI-induced inflammatory stress on bone and the bone marrow niche may activate NF-κB leading to accelerated bone loss. Targeted inhibition of these signaling pathways may reverse TBI-induced bone loss and reduce fracture rates.

Very Long-Chain C24:1 Ceramide Is Increased in Serum Extracellular Vesicles with Aging and Can Induce Senescence in Bone-Derived Mesenchymal Stem Cells

Extracellular vesicles (EVs), including exosomes and microvesicles, function in cell-to-cell communication through delivery of proteins, lipids and microRNAs to target cells via endocytosis and membrane fusion. These vesicles are enriched in ceramide, a sphingolipid associated with the promotion of cell senescence and apoptosis. We investigated the ceramide profile of serum exosomes from young (24⁻40 yrs.) and older (75⁻90 yrs.) women and young (6⁻10 yrs.) and older (25⁻30 yrs.) rhesus macaques to define the role of circulating ceramides in the aging process. EVs were isolated using size-exclusion chromatography. Proteomic analysis was used to validate known exosome markers from Exocarta and nanoparticle tracking analysis used to characterize particle size and concentration. Specific ceramide species were identified with lipidomic analysis. Results show a significant increase in the average amount of C24:1 ceramide in EVs from older women (15.4 pmol/sample) compared to those from younger women (3.8 pmol/sample). Results were similar in non-human primate serum samples with increased amounts of C24:1 ceramide (9.3 pmol/sample) in older monkeys compared to the younger monkeys (1.8 pmol/sample). In vitro studies showed that primary bone-derived mesenchymal stem cells (BMSCs) readily endocytose serum EVs, and serum EVs loaded with C24:1 ceramide can induce BMSC senescence. Elevated ceramide levels have been associated with poor cardiovascular health and memory impairment in older adults. Our data suggest that circulating EVs carrying C24:1 ceramide may contribute directly to cell non-autonomous aging.

miR-219a-5p Regulates Rorβ During Osteoblast Differentiation and in Age-related Bone Loss

Developing novel approaches to treat skeletal disorders requires an understanding of how critical molecular factors regulate osteoblast differentiation and bone remodeling. We have reported that (1) retinoic acid receptor-related orphan receptor beta (Rorβ) is upregulated in bone samples isolated from aged mice and humans in vivo; (2) Rorβ expression is inhibited during osteoblastic differentiation in vitro; and (3) genetic deletion of Rorβ in mice results in preservation of bone mass during aging. These data establish that Rorβ inhibits osteogenesis and that strict control of Rorβ expression is essential for bone homeostasis. Because microRNAs (miRNAs) are known to play important roles in the regulation of gene expression in bone, we explored whether a predicted subset of nine miRNAs regulates Rorβ expression during both osteoblast differentiation and aging. Mouse osteoblastic cells were differentiated in vitro and assayed for Rorβ and miRNA expression. As Rorβ levels declined with differentiation, the expression of many of these miRNAs, including miR-219a-5p, was increased. We further demonstrated that miR-219a-5p was decreased in bone samples from old (24-month) mice, as compared with young (6-month) mice, concomitant with increased Rorβ expression. Importantly, we also found that miR-219a-5p expression was decreased in aged human bone biopsies compared with young controls, demonstrating that this phenomenon also occurs in aging bone in humans. Inhibition of miR-219a-5p in mouse calvarial osteoblasts led to increased Rorβ expression and decreased alkaline phosphatase expression and activity, whereas a miR-219a-5p mimic decreased Rorβ expression and increased osteogenic activity. Finally, we demonstrated that miR-219a-5p physically interacts with Rorβ mRNA in osteoblasts, defining Rorβ as a true molecular target of miR-219a-5p. Overall, our findings demonstrate that miR-219a-5p is involved in the regulation of Rorβ in both mouse and human bone. © 2018 American Society for Bone and Mineral Research.

The Emerging Roles of microRNAs in Stem Cell Aging

Aging is the continuous loss of tissue and organ function over time. MicroRNAs (miRNAs) are thought to play a vital role in this process. miRNAs are endogenous small noncoding RNAs that control the expression of target mRNA. They are involved in many biological processes such as developmental timing, differentiation, cell death, stem cell proliferation and differentiation, immune response, aging and cancer. Accumulating studies in recent years suggest that miRNAs play crucial roles in stem cell division and differentiation. In the present chapter, we present a brief overview of these studies and discuss their contributions toward our understanding of the importance of miRNAs in normal and aged stem cell function in various model systems.

Extracellular vesicle and mesenchymal stem cells in bone regeneration: recent progress and perspectives

Transplanting mesenchymal stem cells (MSCs) has been widely perceived as an ideal treatment for bone repair and regeneration, owing to their differential potential. However, researchers found that very few intravenous MSCs could stay in the target tissue, whereas the majority of them are trapped in liver, spleen, and lung, largely reducing its therapeutic effects. Recently, extracellular vesicles (EVs) have attracted increased attention due to their function in bone repair and advantages over traditional cell therapy. Also, MSCs-derived EVs are likely to achieve the osteogenic goal via modulating the cells and cytokines involved in bone metabolism. This review aims at summarizing the function of EVs and MSCs in bone metabolism and regeneration. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 243-250, 2019.

Differential Expression Profiles of Circular RNAs During Osteogenic Differentiation of Mouse Adipose-Derived Stromal Cells

Osteogenesis is a complex and tightly regulated process. Circular RNAs (circRNAs) are covalently closed RNA molecules which are thought to play a significant role in bone metabolism. The purpose of this study was to investigate the expression and putative function of circRNAs during the osteogenic differentiation of mouse adipose-derived stromal cells (mADSCs). circRNA microarrays were used to determine differential circRNAs expression at different stages during osteogenesis of mADSCs. The most frequent differentially expressed circRNAs were selected by Venn analysis and clustered among the three induced groups. In addition, bioinformatic analyses (gene ontology, pathway, and co-expression network analysis) were used to further investigate these differentially expressed circRNAs. A total of 14,236 circRNAs were detected, of which 43 circRNAs (40 upregulated) were consistently altered at indicated time points during osteogenic differentiation of mADSCs. The exonic circRNAs represented a significantly larger proportion among the differentially expressed circRNAs compared to other types of circRNAs. Gene ontology and Kyoto Encyclopedia of Genes and Genomes biological pathway analysis were performed to evaluate the functions of differentially expressed circRNAs during the osteogenic process. Our circRNA-miRNA co-expression network showed that miR-338-3p was correlated with upregulation of two circRNAs (mmu_circRNA_013422, mmu_circRNA_22566). Our data on circRNA expression profiles may provide valuable insight into circRNA function during osteogenic differentiation of mADSCs. Additionally, the circRNA-miRNA-mRNA pathways may provide information on novel mechanisms and targets for clinical investigations on bone formation and regeneration.

Therapeutic potential of microRNAs in osteoporosis function by regulating the biology of cells related to bone homeostasis

MicroRNAs (miRNAs) are novel regulatory factors that play important roles in numerous cellular processes through the posttranscriptional regulation of gene expression. Recently, deregulation of the miRNA-mediated mechanism has emerged as an important pathological factor in osteoporosis. However, a detailed molecular mechanism between miRNAs and osteoporosis is still not available. In this review, the roles of miRNAs in the regulation of cells related to bone homeostasis as well as miRNAs that deregulate in human or animal are discussed. Moreover, the miRNAs that act as clusters in the biology of cells in the bone microenvironment and the difference of some important miRNAs for bone homeostasis between bone and other organs are mentioned. Overall, miRNAs that contribute to the pathogenesis of osteoporosis and their therapeutic potential are considered.

Emerging roles of extracellular vesicles in cardiac repair and rejuvenation

Cell therapy has received significant attention as a therapeutic approach to restore cardiac function after myocardial infarction. Accumulating evidence supports that beneficial effects observed with cell therapy are due to paracrine secretion of multiple factors from transplanted cells, which alter the tissue microenvironment and orchestrate cardiac repair processes. Of these paracrine factors, extracellular vesicles (EVs) have emerged as a key effector of cell therapy. EVs regulate cellular function through the transfer of cargo, such as microRNAs and proteins, which act on multiple biological pathways within recipient cells. These discoveries have led to the development of cell-free therapies using EVs to improve cardiac repair after a myocardial infarction. Here, we present an overview of the current use of EVs to enhance cardiac repair after myocardial infarction. We also discuss the emerging use of EVs for rejuvenation-based therapies. Finally, future directions for the use of EVs as therapeutic agents for cardiac regenerative medicine are also discussed.

Exchange of genetic material: a new paradigm in bone cell communications

An emerging concept in intercellular communication in mammals is that communication can be mediated by exchange of genetic material, mainly in the form of RNAs. In this review, we discuss recent studies that describe the trafficking of genetic material with a focus on bone cell communication. Three major carriers are discussed: gap junctions, protein-binding complexes, and genetic material exchange mediated by extracellular vesicles. While protein-level exchange has been well documented, no review has summarized the novel paradigm of cell-to-cell communication by genetic information exchange in bone tissues or its biological relevance in terms of bone homeostasis and bone-related diseases. The purpose of this review is to promote further understanding of this novel discovery regarding bone cell communication and provide references for further investigations.

Extracellular microRNAs and oxidative stress in liver injury: a systematic mini review

Recent evidence has suggested that extracellular microRNAs have crucial roles in intercellular communications and are promising as minimally invasive biomarkers for various diseases including cancers. Oxidative stress also plays an essential role in homeostasis and disease development. This systematic review aims to clarify the current evidence on the interaction between oxidative stress and extracellular microRNAs. We identified 32 studies that provided information regarding the association between oxidative stress and extracellular microRNAs: 9 focused on the central nervous system, 11 focused on cardiovascular diseases, and 4 focused on liver injury. Endothelial cell-specific miR-126-3p was the most studied extracellular miRNA associated with oxidative stress. In addition, we highlight some reports that describe the mechanisms of how oxidative stress affects extracellular microRNA profiles in liver injury. In liver injury, the levels of miR-122-5p, miR-192-5p, miR-223-3p, and miR-1224-5p were reported to be elevated in the sera. The release of miR-122-5p, miR-192-5p, and miR-1224-5p from hepatocytes may be attributed to oxidative stress. miR-223-3p could be released from neutrophils and suppress oxidative stress in the liver. Elucidation of the mechanisms of the interaction between extracellular microRNAs and oxidative stress would improve our pathophysiological understanding as well as future medical practice.

Emerging roles of extracellular vesicles in cellular senescence and aging

Cellular senescence is a cellular program that prevents the proliferation of cells at risk of neoplastic transformation. On the other hand, age-related accumulation of senescent cells promotes aging at least partially due to the senescence-associated secretory phenotype, whereby cells secrete high levels of inflammatory cytokines, chemokines, and matrix metalloproteinases. Emerging evidence, however, indicates that extracellular vesicles (EVs) are important mediators of the effects of senescent cells on their microenvironment. Senescent cells secrete more EphA2 and DNA via EVs, which can promote cancer cell proliferation and inflammation, respectively. Extracellular vesicles secreted from DNA-damaged cells can also affect telomere regulation. Furthermore, it has now become clear that EVs actually play important roles in many aspects of aging. This review is intended to summarize these recent progresses, with emphasis on relationships between cellular senescence and EVs.

Emerging Role of Extracellular Vesicles in Bone Remodeling

Extracellular vesicles (EVs), as nanometer-scale particles, include exosomes, microvesicles, and apoptotic bodies. EVs are released by most cell types, such as bone marrow stem cells, osteoblasts, osteoclasts, and immune cells. In bone-remodeling microenvironments, EVs deliver specific proteins (e.g., tenascin C and Sema4D), microRNAs (e.g., miR-214-3p, miR-183-5p, and miR-196a), and other growth factors (e.g., bone morphogenetic protein 1 to 7 and transforming growth factor β1) to osteoblasts and regulate bone formation. In addition, EVs can deliver cytokines, such as RANK (receptor activator of nuclear factor κB) and RANKL (RANK ligand), and microRNAs, such as miR-218 and miR-148a, to modulate osteoclast differentiation during bone resorption. EVs also transfer bioactive molecules and have targeted therapies in bone-related diseases. Moreover, bioactive molecules in EVs are biomarkers in bone-related diseases. We highlight the emerging role of EVs in bone remodeling during physiologic and pathologic conditions and summarize the role of EVs in tooth development and regeneration. At the end of this review, we discuss the challenges of EV application in the treatment of bone diseases.

Extracellular vesicles in the hematopoietic microenvironment

Self-renewal and differentiation are defining characteristics of hematopoietic stem and progenitor cells, and their balanced regulation is central to lifelong function of both blood and immune systems. In addition to cell-intrinsic programs, hematopoietic stem and progenitor cell fate decisions are subject to extrinsic cues from within the bone marrow microenvironment and systemically. Yet, many of the paracrine and endocrine mediators that shape hematopoietic function remain to be discovered. Extracellular vesicles serve as evolutionarily conserved, constitutive regulators of cell and tissue homeostasis, with several recent reports supporting a role for extracellular vesicles in the regulation of hematopoiesis. We review the physiological and pathophysiological effects that extracellular vesicles have on bone marrow compartmental function while highlighting progress in understanding vesicle biogenesis, cargo incorporation, differential uptake, and downstream effects of vesicle internalization. This review also touches on the role of extracellular vesicles in hematopoietic stem and progenitor cell fate regulation and recent advances in therapeutic and diagnostic applications of extracellular vesicles in hematologic disorders.

Mesenchymal stem cell-derived exosomes have altered microRNA profiles and induce osteogenic differentiation depending on the stage of differentiation

Human mesenchymal stem cell (hMSC)-derived exosomes have shown regenerative effects, but their role in osteogenesis and the underlying mechanism are yet to be determined. In this study, we examined the time-course secretion of exosomes by hMSCs during the entire process of osteogenic differentiation. Exosomes derived from hMSCs in various stages of osteogenic differentiation committed homotypic cells to differentiate towards osteogenic lineage, but only exosomes from late stages of osteogenic differentiation induced extracellular matrix mineralisation. Exosomes from expansion and early and late stages of osteogenic differentiation were internalised by a subpopulation of hMSCs. MicroRNA profiling revealed a set of differentially expressed exosomal microRNAs from the late stage of osteogenic differentiation, which were osteogenesis related. Target prediction demonstrated that these microRNAs enriched pathways involved in regulation of osteogenic differentiation and general mechanisms how exosomes exert their functions, such as "Wnt signalling pathway" and "endocytosis". Taken together, the results show that MSCs secrete exosomes with different biological properties depending on differentiation stage of their parent cells. The exosomal cargo transferred from MSCs in the late stage of differentiation induces osteogenic differentiation and mineralisation. Moreover, it is suggested that the regulatory effect on osteogenesis by exosomes is at least partly exerted by exosomal microRNA.

Deduction of Novel Genes Potentially Involved in Osteoblasts of Rheumatoid Arthritis Using Next-Generation Sequencing and Bioinformatic Approaches

The role of osteoblasts in peri-articular bone loss and bone erosion in rheumatoid arthritis (RA) has gained much attention, and microRNAs are hypothesized to play critical roles in the regulation of osteoblast function in RA. The aim of this study is to explore novel microRNAs differentially expressed in RA osteoblasts and to identify genes potentially involved in the dysregulated bone homeostasis in RA. RNAs were extracted from cultured normal and RA osteoblasts for sequencing. Using the next generation sequencing and bioinformatics approaches, we identified 35 differentially expressed microRNAs and 13 differentially expressed genes with potential microRNA–mRNA interactions in RA osteoblasts. The 13 candidate genes were involved mainly in cell–matrix adhesion, as classified by the Gene Ontology. Two genes of interest identified from RA osteoblasts, A-kinase anchoring protein 12 (AKAP12) and leucin rich repeat containing 15 (LRRC15), were found to express more consistently in the related RA synovial tissue arrays in the Gene Expression Omnibus database, with the predicted interactions with miR-183-5p and miR-146a-5p, respectively. The Ingenuity Pathway Analysis identified AKAP12 as one of the genes involved in protein kinase A signaling and the function of chemotaxis, interconnecting with molecules related to neovascularization. The findings indicate new candidate genes as the potential indicators in evaluating therapies targeting chemotaxis and neovascularization to control joint destruction in RA.

Emerging role of extracellular vesicles in musculoskeletal diseases

Research into the biology of extracellular vesicles (EVs), including exosomes and microvesicles, has expanded significantly with advances in EV isolation techniques, a better understanding of the surface markers that characterize exosomes and microvesicles, and greater information derived from -omics approaches on the proteins, lipids, mRNAs, and microRNAs (miRNAs) transported by EVs. We have recently discovered a role for exosome-derived miRNAs in age-related bone loss and osteoarthritis, two conditions that impose a significant public health burden on the aging global population. Previous work has also revealed multiple roles for EVs and their miRNAs in muscle regeneration and congenital myopathies. Thus, EVs appear to be involved in a number of degenerative conditions that impact the musculoskeletal system, indicating that the musculoskeletal system is an excellent model for investigating the role of EVs in tissue maintenance and repair. This review highlights the role of EVs in bone, skeletal muscle, and joint health, including both normal tissue metabolism as well as tissue injury repair and regeneration. A consistent theme that emerges from study of musculoskeletal EVs is that various miRNAs appear to mediate a number of key pathological processes. These findings point to a potential therapeutic opportunity to target EV-derived miRNAs as a strategy for improving musculoskeletal function.

Biogenesis of Pro-senescent Microparticles by Endothelial Colony Forming Cells from Premature Neonates is driven by SIRT1-Dependent Epigenetic Regulation of MKK6

Senescent cells may exert detrimental effect on microenvironment through the secretion of soluble factors and the release of extracellular vesicles, such as microparticles, key actors in ageing and cardiovascular diseases. We previously reported that sirtuin-1 (SIRT1) deficiency drives accelerated senescence and dysfunction of endothelial colony-forming cells (ECFC) in PT neonates. Because preterm birth (PT) increases the risk for cardiovascular diseases during neonatal period as well as at adulthood, we hypothesized that SIRT1 deficiency could control the biogenesis of microparticles as part of a senescence–associated secretory phenotype (SASP) of PT-ECFC and investigated the related molecular mechanisms. Compared to control ECFC, PT-ECFC displayed a SASP associated with increased release of endothelial microparticles (EMP), mediating a paracrine induction of senescence in naïve endothelial cells. SIRT1 level inversely correlated with EMP release and drives PT-ECFC vesiculation. Global transcriptomic analysis revealed changes in stress response pathways, specifically the MAPK pathway. We delineate a new epigenetic mechanism by which SIRT1 deficiency regulates MKK6/p38^MAPK/Hsp27 pathway to promote EMP biogenesis in senescent ECFC. These findings deepen our understanding of the role of ECFC senescence in the disruption of endothelial homeostasis and provide potential new targets towards the control of cardiovascular risk in individuals born preterm.